SB-509 contains the gene (DNA—a kind of biological "blueprint") for a protein. When a study doctor injects SB-509 into the muscles of your neck, arms and/or legs, the drug enters the muscle and nerve cells around the injection sites and causes these cells to make a protein. This protein causes your cells to increase production of one of your own protein called vascular endothelial growth factor(VEGF-A), which may improve the structure and function of nerves and muscles. In addition, there are changes in the levels of 28 additional proteins in your cells. These proteins function to promote the growth of cells, are structures in cells, help synthesize products, and affect immune cells, and some have unknown functions. This increase in your own VEGF proteins may protect and repair the damaged nerves and muscles caused by ALS.